Polyaxial Pedicle Screw Assembly

ABSTRACT

A pedicle fixation assembly and method for assembly comprises a screw head comprising a male bulbous end; a bone fixator component comprising a female concave semi-spherical socket for receiving the screw head; a locking saddle pin for engaging the screw head and the bone fixator component; and a blocker for engaging the screw head and for securing the longitudinal member.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Utility patent applicationSer. No. 11/045,908 filed Jan. 28, 2005, which claims the benefit ofU.S. Provisional Patent Application No. 60/548,543 filed on Feb. 27,2004 and U.S. Provisional Patent Application No. 60/565,658 filed onApr. 27, 2004, whereby the contents of all three applications, in theirentireties, are herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The embodiments of the invention generally relate to medical devices andassemblies, and more particularly to an orthopedic surgical implantassembly used in the field of surgical lumbar, thoracic and cervicalspine treatment.

2. Description of the Related Art

Surgical procedures treating spinal injuries are one of the most complexand challenging surgeries for both the patient and the surgeon. Whenthere are various deformities, trauma, or fractures of the vertebra,surgeons may attempt to “fuse” them together by attaching screw-likedevices into the pedicles of the spine and thereby connecting severalvertebrae (typically two or more) using a semi-rigid rod. However, dueto the complexity of the human anatomy, most surgeons must bend the rod(causing notches thereby reducing fatigue resistance) before placingthem into two or more non-aligned pedicle screws in order to properlystabilize the pedicle screw assembly within the patient's body.

Depending on the purpose of the spine surgery, indications, and patientsize, surgeons must pre-operatively choose between different spinalsystems with differing rod sizes pre-operatively sometimes causingdelays in surgery while waiting for more adequate systems to besterilized. Some surgeons prefer monoaxial screws for rigidity, whilesome sacrifice rigidity for surgical flexibility in screw placement.Therefore, a system is needed to accommodate both theories. For example,during scoliosis surgery conventional polyaxial systems typically cannotlock into a desired position to persuade the spinal column into desiredcorrection before final construct assembly.

Most conventional top loading polyaxial spine screws do not do enough toaddress cantilever failure of the assembly components. Additionally,most polyaxial screws generally do not offer enough flexibility becausethe rod sits too closely on top of the center of rotation. Furthermore,most top loading screw systems generally do not accommodate differentrod sizes. Thus, there remains a need for a new and improved pediclescrew assembly capable of overcoming the limitations of the conventionaldesigns thereby providing the surgeon with improved intra-operativeflexibility and the patient with an improved prognosis for better andcomplete rehabilitation.

SUMMARY OF THE INVENTION

In view of the foregoing, an embodiment of the invention provides anassembly comprising a screw head comprising a bulbous end; a fixatorcomponent configured for receiving the bulbous end of the screw head; apin mounted in the screw head; and a blocker adapted to engage the screwhead. The screw head comprises a slot configured for receiving alongitudinal member. The fixator component comprises a concave socketconfigured for receiving the bulbous end of the screw head. In oneembodiment, the fixator component comprises a threaded end opposite theconcave socket and configured for attaching to a bone. Preferably, thepin engages the fixator component and a bottom portion of thelongitudinal member. Preferably, the blocker secures a top portion ofthe longitudinal member.

Preferably, the pin comprises an upper saddle portion and a lower tipportion. Additionally, according to one embodiment, the pin comprises amulti-part assembly. The pin may be made of one part that may be coatedor it can be made of two parts (an upper and lower portion) comprisingdifferent materials, with the lower portion comprising a mechanicallyharder material than the upper portion. The screw head and the fixatorcomponent comprise a first material, and the lower tip portion of thepin comprises a material having a higher material hardness andcompressive yield strength than the first material. The assembly mayfurther comprise a wear resistant ceramic coating over the screw headand the fixator component.

Preferably, the screw head further comprises two opposed upright endsseparated by the slot, wherein each of the opposed upright ends comprisean inner wall and an outer wall, wherein the inner wall comprises wallthreads, and wherein the outer wall comprises grooves. Preferably, theblocker comprises blocker threads configured around an outer perimeterof the blocker, the blocker threads being dimensioned and configured tomate with the wall threads. The upper saddle portion of the pin maycomprise a slot or slots. The bulbous end of the screw head may comprisea plurality of slots terminating at an opening at a tip of the bulbousend. Moreover, the bulbous end of the screw head preferably comprises agap configured to receive the pin. The concave socket of the fixatorcomponent comprises an inner portion adapted to receive the bulbous endof the screw head; and preferably a dimpled outer portion or othergeometries. Preferably, the fixator component comprises any of a bonescrew and a hook.

Another aspect of the invention provides a pedicle fixation assemblycomprising a screw head comprising a male bulbous end; a bone fixatorcomponent comprising a female concave semi-spherical socket forreceiving the screw head; a locking saddle pin for engaging the screwhead and the bone fixator component; and a blocker for engaging thescrew head and for securing the longitudinal member.

Still another aspect of the invention provides a method of assembling apedicle fixation assembly, wherein the method comprises attaching ascrew head to a bone fixator component; securing the bone fixatorcomponent in a bone; securing a locking pin in the screw head; engagingthe locking pin with the bone fixator component; inserting alongitudinal member in the screw head; and inserting a blocker in thescrew head, wherein the screw head comprises a male bulbous end and thebone fixator component comprises a female concave semi-spherical socketfor receiving the screw head. Preferably, the method further comprisescoating the screw head and the bone fixator component with a wearresistant ceramic coating. The bone fixator component may be configuredas any of a bone screw and a hook.

The embodiments of the invention provide a pedicle screw assemblyimplant device, which may be used anteriorly or posteriorly, and whichis capable of being utilized in surgeries to achieve anterior lumbarinterbody fusion, posterior lumbar interbody fusion, transverse lumbarinterbody fusion, correct degenerative disc disease, adult and pediatricscoliosis as a fixation device, and posterior cervical fusion.

The embodiments of the invention provide a polyaxial spinal screw thatcan become rigid similar to a monoaxial screw inter-operatively ondemand. The embodiments of the invention also offer the surgeon morelateral range of motion than conventional products by utilizing thespace under the screw head to provide a bigger arc of rotation.Moreover, the saddle pin component offers the flexibility to use adiametrical range of spinal rods instead of a fixed size rod.

These and other aspects of the embodiments of the invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingpreferred embodiments of the invention and numerous specific detailsthereof, are given by way of illustration and not of limitation. Manychanges and modifications may be made within the scope of theembodiments of the invention without departing from the spirit thereof,and the embodiments of the invention include all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention will be better understood from thefollowing detailed description with reference to the drawings, in which:

FIG. 1 illustrates an exploded view of the screw assembly according toan embodiment of the invention;

FIG. 2 illustrates an exploded view of the screw assembly during a stepin the manufacturing according to an embodiment of the invention;

FIG. 3 illustrates an exploded view of the screw assembly during a stepin the manufacturing according to an embodiment of the invention;

FIG. 4 illustrates an exploded view of the screw assembly during a stepin the manufacturing according to an embodiment of the invention;

FIG. 5 illustrates a perspective view of the fully assembled screwassembly in a monoaxial position according to an embodiment of theinvention;

FIG. 6 illustrates a perspective view of the fully assembled screwassembly in a polyaxial position according to an embodiment of theinvention;

FIG. 7 is a partial internal view of the screw assembly in a monoaxialposition according to an embodiment of the invention;

FIG. 8 is a partial internal view of the screw assembly in a polyaxialposition according to an embodiment of the invention;

FIGS. 9A through 9H are isolated views of the screw head according to anembodiment of the invention;

FIG. 10A is a perspective view of a bone fixator assembly according to asecond embodiment of the invention;

FIG. 10B is a detailed view of the hook of the bone fixator assembly ofFIG. 10A according to the second embodiment of the invention;

FIGS. 11A through 11B are detailed views of the saddle pin according toa first embodiment of the invention;

FIGS. 12A through 12B are detailed views of the saddle pin according toa second embodiment of the invention;

FIGS. 13 through 14 a are detailed views of the saddle pin according toa third embodiment of the invention;

FIGS. 15A through 15C are detailed views of the blocker according to anembodiment of the invention; and

FIG. 16 is a flow diagram illustrating a preferred method according toan embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The embodiments of the invention and the various features andadvantageous details thereof are explained more fully with reference tothe non-limiting embodiments that are illustrated in the accompanyingdrawings and detailed in the following description. It should be notedthat the features illustrated in the drawings are not necessarily drawnto scale. Descriptions of well-known components and processingtechniques are omitted so as to not unnecessarily obscure theembodiments of the invention. The examples used herein are intendedmerely to facilitate an understanding of ways in which the embodimentsof the invention may be practiced and to further enable those of skillin the art to practice the embodiments of the invention. Accordingly,the examples should not be construed as limiting the scope of theembodiments of the invention.

As mentioned, there remains a need for a new and improved pedicle screwassembly capable of overcoming the limitations of the conventionaldesigns thereby providing the surgeon with improved intra-operativeflexibility and the patient with an improved prognosis for better andcomplete rehabilitation. The embodiments of the invention address thisneed by providing an improved polyaxial pedicle screw device and methodof assembly capable of accommodating multiple rod diameters andwithstanding higher failure strengths. Referring now to the drawings andmore particularly to FIGS. 1 through 16 where similar referencecharacters denote corresponding features consistently throughout thefigures, there are shown preferred embodiments of the invention.

FIGS. 1 through 6 provide an exploded view of the pedicle screw assembly1 according to a first embodiment of the invention. The screw assembly 1comprises a bone screw (fixator component) 10 having a threaded end 11for engaging a bone (not shown) and a concave female socket end 12 forengaging and receiving the screw head 20.

As implemented, the screw head 20 is first snapped into place in thebone screw 10 as shown in FIG. 2. Then, as shown in FIGS. 3 and 9B, thesaddle pin 30 snaps into place in the lower base portion 25 of the screwhead 20, which includes a groove 26 (best seen in FIG. 7) for receivingthe saddle pin 30. In the manufacturing process, once the saddle pin 30snaps into place, the screw assembly 1 is prepared for ultra soniccleaning to remove any impurities and subsequently may be shipped inthis manufactured format (with the saddle pin 30 connected to the screwhead 20, which is connected to the bone screw 10).

FIG. 7 shows that the female spherical socket 12 of the bone screw 10has an undercut 7 to allow the screw head 20 to pivot freely but not todisassemble once the saddle pin 30 is inserted. The thread 11 of thebone screw 10 may be a multiple lead thread to allow faster insertioninto a bone. This thread 11 may be tapered on the minor diameter whilecylindrical on the major diameter to allow a new “bite” with every turnand to accommodate more thread depth towards the bottom of the bonescrew 10 for the cancellous bone.

Once the bone screw 10 is inserted into the bone, a longitudinal member50, which may be embodied as a rod, bar, etc. and blocker 40 areinserted into the screw assembly 1, as illustrated in FIG. 4. The screwhead 20 can accommodate 5.5 mm as well as 6.0 mm rods, which isadvantageous over conventional screw assemblies that are limited toaccepting only rods of a uniform dimension. FIG. 5 illustrates theassembled view of the screw assembly 1 in the straight monoaxialdirection. The threads 11 of the bone screw 10 are double lead, whichprovides greater surface contact with the bone, but drives at 4mm/revolution. FIG. 6 illustrates the screw assembly 1 in a rotationallyarticulated position. The maximum angulation is 25 degrees/side, but themedial correction/travel of the longitudinal member 50 is 3.8 mm/side,which is nearly twice of what most conventional screws offer.

In FIG. 7, the locking mechanism of the screw assembly 1 is illustrated.Here, a two step locking process is shown. The first position expandsthe screw head 20 into the bone screw 10, and the second positionpermanently turns the polyaxial screw assembly 1 into a monoaxial screwassembly 1 by using the saddle pin 30 to lock the assembly 1. As FIG. 8demonstrates, the screw assembly 1 can be permanently locked in anydesired position (within the 25 degree guideline) simply by sending thelongitudinal member 50 “home” or by using a tool (not shown) to lock theassembly 1 at the desired angle.

FIG. 9A illustrates the overall configuration of the screw head 20. FIG.9B illustrates a front view of the screw head 20. FIG. 9C is across-sectional view from cut-line “CC” of FIG. 9D. FIG. 9E is across-sectional view from cut-line “BB” of FIG. 9F and FIG. 9G is across-sectional view from cut-line “AA” of FIG. 9F. Additionally, FIG.9H is an enlarged detailed view of the encircled area “A” of FIG. 9Gillustrating the threaded inner portion 23 in more detail. As shown inFIGS. 9A through 9H, the screw head 20 includes a bulbous (spherical)male end 21 for engaging the concave female socket 12 of the bone screw10. The screw head 20 also includes a pair of upright ends 22 oppositethe bulbous male end 21, wherein the upright ends 22 comprise a threadedinner portion 23 for engaging the blocker 40. Furthermore, the screwhead 20 includes a generally open U-shaped inner portion 24 forreceiving the saddle pin 30 and the longitudinal member 50. The male end21 of the screw head 20 includes a plurality (for example, four or more)slots 6 that allow the male end 21 to expand into the female sphericalsocket 12 of the bone screw 10 at any allowable angle once the saddlepin 30 is forced through.

Since the screw head 20 is pivoting inside the female socket end 12 ofthe bone screw 10, the assembly 1 is allowed to be inserted deeper intothe bone without having the bone or anatomy prematurely limit the rangeof angulations of the screw head 20. The screw head 20 further includesexternal features or cuts 29 that assist in accommodating surgicalinstrumentation during manipulation and assembly during the surgicalprocedure. These cuts 29 allow various instruments (not shown) to firmlyand positively hold and manipulate the screw head 20 on one side or bothsides of screw head 20.

FIG. 10A is a perspective view of a bone fixator assembly according to asecond embodiment of the invention, wherein the bone fixator componentis configured as a hook 60. The hook 60 is further illustrated in FIG.10B. The hook 60 includes a concave socket 12 having an inner portion 9adapted to receive the bulbous end 21 of the screw head 20; and adimpled outer portion 8. The hook 60 further includes a pair of arms 61,62 connected by a connection arm 64. A space 63 separates the arms 61,62 from one another. The arms 61, 62 are configured to receive anadditional member (not shown) for subsequent attachment to the bone.

The several embodiments of the saddle pin 30 are shown in FIGS. 11Athrough 14. The saddle pin 30 provides a proper seat for thelongitudinal member 50 and avoids notching a typical titaniumlongitudinal member 50 (titanium is very notch sensitive). Furthermore,the saddle pin 30 allows one to accommodate multiple sizes oflongitudinal members 50 in the same screw assembly system 1 which is afirst for a titanium system because of the above-mentioned notchingfactors. The saddle pin 30 is configured with a slot 32 through thecenter to allow expansion of the upper portion (head) 131 of the saddlepin 30. The bottom 35 of the saddle pin head 131 is angled to allow thesaddle pin 30 to accept a larger-sized longitudinal member 50. Thesaddle pin 30 initially expands the male sphere 21 of the screw head 20into the female spherical socket 12 in the bone screw 10 causing thescrew assembly system 1 to lock or start locking (i.e., causing the malesphere 21 of the screw head 20 to lock in the female spherical socket 12of the bone screw 10). The saddle pin 30 then “digs” into the femalespherical socket 12 of the bone screw 10 to provide a secondary lockingforce to avoid bending failure of the assembly 1.

FIGS. 11A through 11B illustrate a first embodiment of the saddle pin30. The saddle pin 30 generally includes an upper portion 131 and alower portion 132. The upper portion includes a slot 32, which isconfigured from the lowest area 33 of the upper portion 131 into theupper area 34 of the lower portion 132 of the saddle pin 30. A secondarylocking mechanism 36 may be configured on the lower portion 132 of thesaddle pin to further achieve locking of the saddle pin 30 once it isinserted in the screw head 20. The lower portion 132 of the saddle pin30 terminates with a pointed end 37 to allow for digging into the femalesocket 12 of the bone screw 10. FIGS. 12A through 12B illustrate asecond embodiment of the saddle pin 30. The difference between the firstand second embodiments of the saddle pin 30 is that the upper portion ofthe saddle pin 131 in the second embodiment includes two generally flatupper opposed ends 38 to more matingly configure with the geometry ofthe screw head 20 and the longitudinal member 50.

FIGS. 13 through 14 illustrate a third embodiment of the saddle pin 30.In particular, in the third embodiment, the saddle pin 30 comprises twoparts: an upper portion 131 preferably comprising titanium and a lowerportion 132 which is preferably ceramic. According to the thirdembodiment, the material of the lower portion 132 of the saddle pin 30is preferably ceramic and has a higher hardness and compressive yieldstrength than the comparative hardness and compressive yield strength ofTi₆Al₄V, which is the material which may be used in constructing thescrew head 20 and bone screw 10.

As shown in FIG. 13, the upper portion 131 of the saddle pin 30 includesa slot 32 in the seat portion 133 and tapered angled ends 134.Preferably, the saddle pin 30; i.e., the upper portion 131 and theceramic tip 132 are assembled last in the overall process. Specifically,the screw head 20 snaps into the bone screw 10. Then, the ceramic tip132 slides into the screw head 20, and finally the titanium saddle(upper portion) 131 is press fitted into the screw head 20 keepingeverything in place and oriented in a relaxed state.

As best seen in FIG. 14, the lower portion 132 of the saddle pinterminates with a series of cascading walls 137, 138 having slopedangles, terminating with the pointed end 37 for attachment into thescrew head 20/bone screw 10 assembly. The material properties of thesaddle pin tip 132 are such that it prevents the deformation on thesaddle pin 30 before the saddle pin 30 gives the proper bending andpenetrating effects onto the screw head 20/bone screw 10 assembly.Examples of the types of materials used for the saddle pin pointed end37 include Zyranox™ and HIP Vitox™, both of which are available fromMorgan Advanced Ceramics, United Kingdom.

The blocker 40, which is further illustrated in FIGS. 15A through 15C,includes a standard buttress thread 41 configured along an outerperimeter of the blocker 40. The blocker 40 helps to secure thelongitudinal member 50 inside the screw head 40. The threads 41 of theblocker 40 are configured to engage the threads 23 of the screw head 20.Additionally, the blocker 40 aids in preventing the expansion of thescrew head 20 when torqued on the longitudinal member 50, directing thecounterforce more vertically than horizontally. The top 42 of theblocker 40 has a fastening feature 43 such as a hex or square lockfeature to allow high torque to be applied in locking the assembly 1.Furthermore, the blocker 40 may be configured with a free rotatingsaddle (not shown) to accommodate, via tangential contact, thelongitudinal member 50 and help to further prevent notching of thetitanium alloy used to construct the longitudinal member 50. Moreover,the blocker 40 may have a “timed” thread 41 that is consistently andprecisely related to the blocker driving tool (not shown) to helpcalculate the torsional and vertical position of the blocker 40 therebyassisting the torque measurement applied to the blocker 40.

Another aspect of the invention is illustrated in the flowchart of FIG.16, which includes descriptions which refer to components provided inFIGS. 1 through 15C. FIG. 16 illustrates a method of assembling apedicle screw assembly 1, wherein the method comprises attaching (200) ascrew head 20 to a bone fixator component 10; securing (210) the bonefixator component 10 in the bone (not shown); securing (220) a saddlepin 30 in the screw head 20; engaging (230) the saddle pin 30 with thebone fixator component 10; inserting (240) a longitudinal member 50 inthe screw head 20; and inserting (250) a blocker 40 in the screw head20. As mentioned, the embodiments of the invention provide an axialmovement of the screw head up to 25 degrees in any plane. Moreover, theembodiments of the invention allow for greater medial translation of thelongitudinal member 50 (nearly 4 mm compared to the conventional deviceswhich are generally limited to 2 mm).

Moreover, according to an aspect of the invention, the inventiveassembly 1 can be used as a dynamic rod system to complement artificialdiscs. According to this embodiment, the outside of the spherical jointpart 21 of the screw head 20 and the inner spherical surface 9 of thebone screw cup 12 are coated with a wear resistant ceramic coating. Inthis scenario, the saddle pin 30 is not digging into the bone screw 10and in fact is configured at a shorter length than some of the otherembodiments. This system allows some motion instead of rigid fixationand shares the load with the artificial disc disallowing excessiveforces being applied to the artificial disc and increasing itsfunctional life. For example, this occurs as a result of the ceramiccoating, which may be used in the embodiments of the invention. As such,the spherical joint 21 of the screw head 20 and the inner sphericalsurface 12 of the bone screw 10 have lower friction and higher wearresistance characteristics, thus improving the overall characteristicsof the screw assembly 1.

Generally, as shown in FIG. 1 through 15C, the embodiments of theinvention provide an assembly 1 comprising a screw head 20 comprising abulbous end 21; a fixator component 10 configured for receiving thebulbous end 21 of the screw head 20; a pin 30 mounted in the screw head20; and a blocker 40 adapted to engage the screw head 20. The screw head20 comprises a slot 24 configured for receiving a longitudinal member50. The fixator component 10 comprises a concave socket 12 configuredfor receiving the bulbous end 21 of the screw head 20. In a firstembodiment, the fixator component 10 also comprises a threaded end 11opposite the concave socket 12 and configured for attaching to a bone.The pin 30 engages the fixator component 10 and a bottom portion 51 ofthe longitudinal member 50. The blocker 40 secures a top portion 52 ofthe longitudinal member 50. The pin 30 comprises an upper saddle portion131 and a lower tip portion 132.

Additionally, the pin 30 may comprise a multi-part assembly. The uppersaddle portion 131 of the pin 30 comprises titanium and the lower tipportion 132 of the pin 30 comprises a ceramic material. Moreover, thelower tip portion 132 comprises a mechanically harder material than theupper saddle portion 131. The screw head 20 and the fixator component 10comprise a first material, and the lower tip portion 132 of the pin 30comprises a material having a higher material hardness and compressiveyield strength than the first material. The assembly 1 further comprisesa wear resistant ceramic coating (not shown) over the screw head 20 andthe fixator component 10.

The screw head 20 further comprises two opposed upright ends 22separated by the slot 24, wherein each of the opposed upright ends 22comprise an inner wall 27 and an outer wall 28, wherein the inner wall27 comprises wall threads 23, and wherein the outer wall 28 comprisesgrooves (cuts) 29. The blocker 40 comprises blocker threads 41configured around an outer perimeter 42 of the blocker 40, the blockerthreads 41 being dimensioned and configured to mate with the wallthreads 23. The upper saddle portion 131 of the pin 30 comprises a slot32. The bulbous end 21 of the screw head 20 comprises a plurality ofslots 6 terminating at an opening 4 at a tip 3 of the bulbous end 21.Moreover, the bulbous end 21 of the screw head 20 comprises a gap 19configured to receive the pin 30. The concave socket 12 of the fixatorcomponent 10 comprises an inner portion 9 adapted to receive the bulbousend 21 of the screw head 20; and a dimpled outer portion 8. The fixatorcomponent 10 is configured as any of a threaded bone screw 10 (as shownin FIGS. 1 through 8) and a hook 60 (as shown in FIGS. 10A and 10B)according to the several embodiments of the invention.

The embodiments of the invention provide a pedicle screw assemblyimplant device 1, which may be used anteriorly or posteriorly, and whichis capable of being utilized in surgeries to achieve anterior lumbarinterbody fusion, posterior lumbar interbody fusion, transverse lumbarinterbody fusion, correct degenerative disc disease, adult and pediatricscoliosis as a fixation device, and posterior cervical fusion.

Moreover, the embodiments of the invention provide a polyaxial spinalscrew assembly 1 that can become rigid similar to a monoaxial screwinter-operatively on demand. The embodiments of the invention also offerthe surgeon more lateral range of motion than conventional products byutilizing the space under the screw head 20 to provide a bigger arc ofrotation. Moreover, the saddle pin 30 component offers the flexibilityto use a diametrical range of spinal longitudinal members 50 instead ofa fixed size longitudinal member.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without departing from the generic concept,and, therefore, such adaptations and modifications should and areintended to be comprehended within the meaning and range of equivalentsof the disclosed embodiments. It is to be understood that thephraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodiments ofthe invention have been described in terms of preferred embodiments,those skilled in the art will recognize that the embodiments of theinvention can be practiced with modification within the spirit and scopeof the appended claims.

What is claimed is:
 1. A pedicle screw assembly comprising: a screw headcomprising a slot and a bottom portion; a connecting end operativelyconnected to said bottom portion of said screw head; a bone fixatorcomponent comprising a socket that receives said connecting end; meansfor causing engagement of said connecting end to said bone fixatorcomponent; and a blocker that engages said screw head.
 2. The pediclescrew assembly of claim 1, wherein a combination of said bottom portionof said screw head with said connecting end form a substantially bulbousbody.
 3. The pedicle screw assembly of claim 1, wherein said bonefixator component is located completely outside of said screw head. 4.The pedicle screw assembly of claim 1, wherein said bottom portion ofsaid screw head and said connecting end are locked into said socket ofsaid bone fixator component.
 5. The pedicle screw assembly of claim 1,wherein said screw head comprises at least one upright end adjacent tosaid slot.
 6. The pedicle screw assembly of claim 5, wherein said screwhead comprises: a lower base portion adjacent to said at least oneupright end; and an aperture extending from said lower base portionthrough said connecting end.
 7. The pedicle screw assembly of claim 2,wherein substantially bulbous body is rotatable with respect to saidsocket.
 8. An assembly comprising: a slotted screw head comprising asubstantially bulbous body extending away from a bottom portion of saidslotted screw head; a hole in said slotted screw head and extendingthrough said substantially bulbous body; a bone engaging componentcomprising a socket that cups said substantially bulbous body; and meansfor causing outward expansion of said substantially bulbous body.
 9. Theassembly of claim 8, wherein said bone engaging component is locatedcompletely outside of said slotted screw head.
 10. The assembly of claim8, wherein said substantially bulbous body is locked into said socket ofsaid bone engaging component.
 11. The assembly of claim 8, wherein saidslotted screw head comprises at least one upright end pointing away fromsaid substantially bulbous body.
 12. The assembly of claim 11, whereinsaid slotted screw head comprises: a lower base portion adjacent to saidat least one upright end; and an aperture extending from said lower baseportion through said substantially bulbous body.
 13. The assembly ofclaim 8, wherein substantially bulbous body is rotatable with respect tosaid socket.
 14. An assembly comprising: a bone engaging componentcomprising a socket; and a screw head comprising a stem portionextending from a bottom of said screw head and fits inside said socket.15. The assembly of claim 14, further comprising means for locking saidstem portion inside said socket.
 16. The assembly of claim 14, whereinsaid stem portion is located completely outside of said screw head. 17.The assembly of claim 14, wherein said screw head is rotatable withrespect to said bone engaging component.
 18. The assembly of claim 14,wherein said screw head comprises: at least one upright end positionedopposite to said stem portion; a lower base portion adjacent to said atleast one upright end; and an aperture extending from said lower baseportion through said stem portion.
 19. The assembly of claim 18, furthercomprising a pin dimensioned and configured to fit in said aperture. 20.The assembly of claim 14, wherein said stem portion is expandable.